1. Field of the Invention
The present invention relates to an anode active material, a method of producing the same and a lithium battery using the same. More particularly, the invention is directed to an anode active material having high capacity and excellent capacity retention. The invention is also directed to a method of producing the anode active material and to a lithium battery using the anode active material and having a long lifespan.
2. Description of the Related Art
Lithium metal has been used as the anode active material. However, when lithium metal is used, dendrites can form causing battery short-circuits, resulting in a risk of explosion. Accordingly, carbon-based materials are widely used for the anode active material instead of lithium metal.
Examples of carbon-based active materials used for the anode active material in lithium batteries include crystalline-based carbon (such as natural graphite and artificial graphite) and amorphous-based carbon (such as soft carbon and hard carbon). Although amorphous-based carbon has high capacity, charge/discharge reactions are highly irreversible. Natural graphite is the main crystalline-based carbon used, and its theoretical capacity is high (at 372 mAh/g). Therefore, crystalline-based carbon is widely used as an anode active material. However, the cycle life of such batteries may be very short.
The theoretical capacity of about 380 mAh/g of such a graphite or carbon-based active material (which is currently considered a high capacity) may not be sufficient for future lithium batteries that may require higher capacities.
In order to overcome this problem, research has been actively conducted into metal-based anode active materials and intermetallic compound-based anode active materials. For example, research has been conducted into lithium batteries using metals such as aluminum, germanium, silicon, tin, zinc, lead, etc. or semimetals as anode active materials. Such materials have been known to have large capacities, high energy densities, and good intercalation and deintercalation capabilities compared to anode active materials using carbon-based materials. Thus, lithium batteries having large capacities and high energy densities can be prepared using these materials. For example, pure silicon is known to have a high theoretical capacity of 4017 mAh/g.
However, such materials have shorter cycle lifespans than carbon-based materials, and thus cannot be put to practical use. When an inorganic material (such as silicon or tin) is used in the anode active material as a lithium intercalating and deintercalating material, the volume of the inorganic material changes during charge/discharge cycles, resulting in the degradation of conductivity between the active materials or in the detachment of the anode active material from the anode current collector, as shown in FIG. 1. That is, the volume of the inorganic material (such as silicon or tin) increases by about 300 to 400% during charging through the intercalation of lithium, and the volume decreases during discharging through the deintercalation of lithium. Therefore, when charge/discharge cycles are repeated, spaces may be generated between the inorganic particles and the active materials, and electrical insulation may occur, thereby rapidly degrading the cycle life of the battery.
Therefore, a need exists for an anode active material with high capacity and excellent capacity retention properties, and for a lithium battery with a long cycle life employing the anode active material.